Good idea...lets explore!

Your idea of afternoon run in theory sounds okay, but lets explore that further. Assuming the Chama passenger train departs at 10:30 it usually arrives at Cumbres around noon. After turning and watering, etc it departs about 12:30 for CHama. Arrives there about 1:30, and has to turn, and perhaps service, gather train, and perhaps another crew, etc. Figure departing around 3 pm. That might leave 2-3 hours of sun for photography if you are lucky. Figure on straight run to the top is 1.5 hours(actually a little less), then you probably have enough time for 2-3 photos with sun if you get to Coxo in time! A lot of work for little reward!
A better plan would be to hoist a few cars on previous days doubleheaders to Cumbres, and assemble a train there. On the 23rd you would start the special train at Cumbres at 12:30(folks could park at Cumbres). Turn engine and back special behind the passenger special to Osier. Then do runbys from Osier to Cumbres the rest of the Afternoon. At least this way you get good sun on the WB trip from Osier to Cumbres, and see something more than the usual stuff from Chama to Cumbres.
Also, in the event another loco is ready(say 484) you could start the charter in the morning in Chama with that engine, and pick-up more cars at Cumbres. If the extra engine isn't ready, you have your plan B waiting at Cumbres. At least these are alternatives.
Steamingly,
Greg Scholl